Research On Power Allocation Method Of High-speed Railway Wireless Communication System

In order to further improve the transmission quality of high-speed railway vehicle ground communication system,in this thesis,based on single antenna system,distributed antenna system(DAS)and large-scale multiple input multiple output(MIMO)system respectively,the optimization of energy efficiency and transmission quality of service of the "two hop" vehicle ground communication link in high-speed railway scenario are studied.Firstly,aiming at the single antenna vehicle ground communication link,this thesis studies how to improve the energy efficiency of the high-speed rail communication system through reasonable power allocation.The matching problem of data arrival process and wireless transmission process for the uplink link of single antenna system is considered.The energy efficiency of the uplink system is optimized under the limitation of the maximum transmission power and the minimum receiving rate.The Lagrange multiplier method is used to solve the optimization problem,updating Lagrange multipliers by bisection method,then the optimal solution is obtained and the power distribution of the system at each time is determined.In view of the problem of high complexity of the solution,the optimization algorithm should be improved,so based on the discussion of the feasible region of the optimal solution,a low complexity optimization algorithm is proposed.In addition,the effectiveness of the low complexity algorithm is verified by simulations.Then,for the distributed antenna system,the energy efficiency of the downlink transmission system is optimized with the delay constraint considered.A method of transmission mode selection and power optimization is proposed.Based on the the power allocation,the appropriate remote antenna units(RAU)are selected to provide services for the train by utilizing the characteristics of the distributed antennas.The maximum energy efficiency values of different transmission modes are compared,and the optimal transmission mode for each time is determined to further enhance the maximum energy efficiency of the system.Through the simulation,the feasibility and effectiveness of the transmission mode selection scheme are verified.Finally,aiming at the large-scale MIMO vehicle underground communication scenario,a beam assignment and power allocation scheme for the quality of service of the carriage is proposed.Beamforming technology is utilized to concentrate the energy to the main lobe for transmission to reduce the power loss,and then the beam and power allocation at the transmitter are optimized to ensure the fairness of the receiving rate of each carriage and improve the communication service of the train.The simulation results show that the scheme not only meets the speed requirements of each carriage,but also effectively improves the mobile service of the system.